It is required to downsize an acoustic wave device used as a filter, a duplexer or the like in mobile communication equipment. An acoustic wave element for the acoustic wave device may be a surface acoustic wave (SAW) device or a piezoelectric thin-film resonator. The SAW device has a piezoelectric substrate on which an interdigital transducer (IDT) is formed. The piezoelectric thin-film resonator, which is frequently called film bulk acoustic resonator (FBAR), has a piezoelectric thin film sandwiched between electrodes. For example, Japanese Patent Application Publication No. 2004-64599 discloses an arrangement in which a SAW device is face-down mounted on a base substrate, and an IDT formed on a piezoelectric substrate is hermetically sealed with a bonding member such as solder provided on a peripheral portion of the piezoelectric substrate.
A conventional acoustic wave device has a possibility that solder for sealing and/or solder bump electrodes used along with solder for sealing may cause a short-circuit between IDT electrode fingers and/or a deterioration of the characteristics.